Toxicity of spinosad was primarily evaluated with three bioassay methods: feeding, spraying (Residual exposure) and combination with larval medium against one susceptible and one field population. Feeding method was selected as efficient method for survey of susceptibility or resistance of seven field populations. In feeding bioassay method, spinosad LD₅₀ of susceptible strain at 24h and 72h were 3.78 and 1.54 g (AI) per gram bait and for LD₉₅ were 5.59 and 3.35g (AI) /g, respectively. LD₅₀ of field populations at 24h ranged  from 3.974- 4.303 and for LD₉₅ from 7.33- 8.30 g (AI)/gr. LD₅₀ at 72h ranged from 1.54- 1.72g/gr and LC₉₅ were 3.31- 3.93 g /g, respectively. Determination of lethal dose ratios with lower and upper limits indicated no significant difference between spinosad LD₅₀ of susceptible and field population at 24h and 72h. In Residual method, spinosad LDof susceptible and field population (AHDS) at 24h were 0.015 and 0.016 and for LD₉₅ were 0.03, 0.033 g (AI) per m², respectively. At 72h, LDwere 0.0065, 0.007 and LD₉₅ were 0.014, 0.015 g (AI)/ m² for the above populations. In combination of spinosad with larval medium, LD and LD₉₅ of susceptible population were 9.79 and 29.5 mg (AI) per kg medium. For field population (AHDS), LDand LD₉₅ were 9.95 and 56.6 mg (AI)/kg. There was no significant difference at LDof susceptible and field population with these two methods. Totally, the result of this study indicated that LD₅₀ values decrease approximately 2-3-fold between 24 and 72 h and all field populations were susceptible to spinosad.